In order for a recessive mutation to be visually apparent, the snake will need two copies of the recessive genes. They get one copy from each parent. Ultra is a hybrid gene. Most corn snake genes are recessive, so in order to get a visually amel snake, there would be two copies of the amel gene sitting at the amel locus. It just so happens that the rat snake gene for ultra also sits at the same place as the amel gene. So if the parent is visually ultramel, it means that there is one gene for ultra and one gene for amel, both sitting at the same locus. You couldn’t get a homozygous ultra baby from your pairing, because the ultramel parent can only contribute one ultra gene or one amel gene. So amels are possible, or ultramels (since your snow would contribute the other amel gene). I know genetics can be a bit confusing and I am certainly no geneticist, but I hope that helps!